Ed Jacoby's Level 3 project, "Screaming Yellow Zonker", had been ready to fly for at least 6 months. But, a combination of no rain/burn bans, too much rain/flooded fields, no waiver, no time, and finally a broken arm resulted in the flight being delayed repeatedly. Finally, on June 3rd 2001, everything came together at the same time. The location was a private field near Eden, Texas. Weather conditions were clear with winds blowing 15 - 20 mph from the south. We launched from a clear spot in a field with trees to the south which would result in the rockets drifting into a huge cleared field to the north.

Ed's rocket was scratch built from Hawk Mountain 4 inch fiberglass components. The project utilized dual altimeters using both barometric and inertial data. The dual deployment charges were single fault tolerant and were designed to deploy a tiny drogue at apogee and a main chute at 500 feet. Ed chose a Kosdon M1130 to power the rocket. The 3 inch M1130 uses Kosdon's "slow" propellant, burning for 5.1 seconds while putting out a rated impulse of 5770 newton seconds. Ed used a heavy duty rail launcher to insure a straight boost during the critical first few feet of flight. This would be especially important on a windy day. Predicted altitude was 10,500 feet at a max velocity of mach .98.

Ed "Crip" Jacoby (right) with his launch team before flight.

When all was ready, checked and rechecked, the ignitor was installed and we moved back to a safe distance to wait for the wind to drop off. Finally, the wind dropped off a little, the countdown began and the button was pushed. The ignitor fired instantly and the motor immediately came up to full power and the flight was on it's way! Even though the wind was blowing around 15 mph as the rocket cleared the tower, there was no evidence of any weather cocking. The big rocket accelerated fast and continued to boost vertical. The motor burned out after 5 seconds and the rocket began it's long coast upward, trailing a thick cloud of tracking smoke produced by Kosdon's full 3 inch diameter smoke charge. The rocket's tracking smoke was easily visible to the unaided eye over 2 miles straight up. Right at apogee the charges fired, releasing the drogue chute and a red cloud of paint pigment. The rocket began a fast but controlled fall to earth, not drifting significantly as it fell.

At around 500 feet the main deployment charge fired, the main chute was ejected from the rocket, and......OH NO!.......it remained in a tight little ball and never opened. The rocket impacted under drogue only, smashing through a tree on the way down and was.....sigh.....totally destroyed. Upon reaching the impact site, it was obvious what had happened. Though the recovery system was carefully packed with the shock cord resting on top of the piston and the parachute resting on top of the shock cord, when the ejection charge fired the shock cord somehow looped itself TWICE around the chute. As the shock cord stretched out, one loop passed under the other loop, making a tight knot that would not allow the chute to open.

"Screaming Yellow Zonker" screams upward, powered by a Kosdon M1130.

Though the airframe was totally smashed, the altimeters and radio transmitter survived. Altimeter data indicated the rocket reached a max altitude of 10,810 feet and a max velocity of 663 mph (mach 1). Max loading was 8.3 Gs. Max velocity occurred at 2,320 feet at 4.2 seconds after liftoff.

The flight in a word? Bummer. After a perfect flight, a random moment of bad luck doomed the mission. We couldn't get that shock cord to tie itself in a knot around that chute again if we tried. There is always some tiny amount of luck required for our hobby (or any hobby). We use our skill and experience to design rockets that minimize the need for luck, but we will always have the rare failure because of "bad luck". Perhaps this failure could have been prevented by the use of a chute bag, but the chute bags produce their own failure modes, namely getting the chute out of the bag. There's just no such thing as a "guaranteed to work" flight. Just ask NASA.

And now for the GOOD news...

Since this was a private launch and there were no "innocent bystanders" around, Tom Montemayor decided to put up a high risk shot. This would be a Hawk Mountain Bad Attitude powered by a Kosdon L850. Tom considered the flight "high risk" because this was an original Bad Attitude kit with .092 fin thickness (rather than the current .125) and the fins were much larger than the current models.

With the fins being large and thin, Tom felt certain the fins would flutter. Of course, fin flutter doesn't necessarily cause a flight to fail. As long as the fins remain securely attached, the flight should continue straight. Fluttering causes drag to significantly increase, and if it continues long will eventually cause the G10 to fail. Tom felt his "through the wall" fins were securely attached and didn't think the duration of flutter would be long enough to degrade the G10.

The Kosdon L850 is a 54mm baby L. Burn time is 2.9 seconds putting out a total impulse of 2,700 newton seconds. The motor case is over 29 inches long. Computer simulations predicted a max altitude of 7,700 feet and a max velocity of mach 0.9.

Tom Montemayor shows off his "Bad Attitude" before flight.

The rocket was launched during a lull in the wind, and like Jacoby's rocket lifted off very fast and straight. Less than a second after liftoff, the sky filled with a very distinctive, loud, buzzing sound. It sounded like we had launched a Hypertech hybrid. Of course, the buzzing was the fins fluttering at several thousand cycles per second. I kept waiting to see one or more fins depart the vehicle, but the flight continued straight and true and eventually the buzzing faded away. The barometric altimeter deployed a small streamer at apogee and right at 250 feet the main deployed. The rocket landed safely and undamaged in the cleared field about a mile downrange.

I felt certain that the polyurethane paint would show some evidence of cracking or peeling due to the high frequency flutter. However, careful postflight inspection showed no evidence of any damage to the fin material or to the paint. The rocket looks just as good as it did before the flight! Data downloaded from the Adept altimeter showed a peak altitude of 7,209 feet at a max velocity of 1011 feet/second (mach .92). Max velocity was achieved 2.7 seconds into the flight at an altitude of 1161 feet. Max loading was 8 Gs. The rocket achieved an altitude within 5% of prediction and exceeded predicted velocity by 4%. So, the fin flutter did not affect the rocket as much as I expected. Except for the noise, it was not obvious that any flutter had occurred.

The last flight of the day was put up by Bruce McEwen, who drove in from San Angelo to assist with the launch and to put up his own experimental rocket. Bruce launched a finless "cube" rocket powered by an H128. Stability was provided by 4 rods extending out from the bottom of the cube. Even in the strong winds, the flight was perfect. The cube left the rod straight, reached a max altitude of around 400 feet and deployed it's chute right at apogee. The unique rocket landed safely and undamaged about 50 yards downrange. A great flight!